This invention relates to the sealing of cracks and other points of leakage in joints in underground pipes and mains, and particularly gas mains, and permanent fogging or misting systems for use therein.
The sealing of leaks in gas mains and other underground pipelines presents major problems in an area where demand is growing rapidly due to deterioration of such pipelines, which, in many places such as the United Kingdom and the United States, have been in place and in use for many years. Over that time the pipes, which are mainly cast iron, have become porous or have cracked for a variety of reasons such as age, corrosion, subsidence of surrounding soil, and the passage of heavy trucks and other vehicles over roads under which the underground pipes are buried. This leakage can lead to dangerous situations, and in extreme cases explosion and bodily harm or even fatalities. Moreover, the scale of the problem can be so huge that the digging up and replacement of the old and broken mains becomes an economic impossibility, and in many cases where, for example, the pipeline passes under a building, also a physical impossibility. Therefore, it is of considerable benefit if such pipelines can be repaired, rather than having to be replaced when the pipeline becomes unusable, particularly because of leaks, cracks or fissures in joints.
Various methods have been used and proposed in the past for the repair of underground pipelines. Where the pipeline is accessible, methods have involved exposing the pipeline and either replacing the broken or porous section with a new section, or, where that is not possible or economical, applying a sealant coating, e.g. a polyurethane coating, around the exterior of the pipe.
An alternative method, used particularly on relatively small diameter pipelines such as those supplying gas to domestic premises, is to feed a new, smaller diameter flexible plastics pipe through the gas main, which then simply acts as a conduit to accommodate the smaller diameter plastics replacement pipeline inside the previously existing pipeline, In such a method, the gas supply is to the plastics replacement pipeline, rather than to the existing, broken, cracked or corroded pipeline. This method of inserting a new pipeline inside the old is a quick, easy and inexpensive method of repair, but is of limited applicability because of the reduced capacity of the inserted smaller diameter pipeline, as compared with that of the original pipeline.
Various methods and compositions have also been tried in the past for the in situ repair of underground pipelines. Such methods, in general include using either injection or spraying sealant material inside the pipeline at the point of fracture or a fogging technique in which a sealant is introduced into the pipeline as a fog or mist, the suspended droplets of which deposit on the inside of the pipelines to seal any cracks or fissures therein.
One leakage control technique that has been used is the fogging of gas mains, particularly those having lead-yarn joints, with ethylene glycol or diethylene glycol. These glycol materials swell the yarn in the lead-yarn joints and temporarily regenerate the seals in such joints. However, the problem with glycol based fogs is the temporary nature of the seal, since the glycol is eventually extracted by the gas and leaks can then re-occur. One way to avoid this problem is by employing a gas conditioning system wherein e.g. a monoethylene glycol vapor is supplied to the line on a continuous basis to keep the yarn saturated and in the swelled condition. While this approach has been fairly effective, it does require considerable effort to insure an effective system is being maintained. Additionally, as glycol prices rise, this operation can be somewhat costly because of the need for a constant supply of a glycol material. Therefore, a system providing a permanent seal would be advantageous.
Other fogging systems and sealants such as anaerobic adhesives have been tried and while they could be applied as a fog and provide permanently sealed joints, they enter the mechanical portions of the system, i.e. the seal and lock mechanism associated with gas mains, and stop them from working.
Accordingly, there is the need for an effective and permanent gas sealing system which is particularly useful in the sealing of gas mains and other underground pipelines.